1. Field of the Invention
The invention relates to a network coupling device for a so-called home network, i.e. for a data network which uses cabling actually intended for other purposes, such as for example existing telephone cabling or power supply cabling, as a transmission medium. The invention also relates to a home network with this network coupling device.
For connecting up a number of data processing devices, in particular in the home area, currently a technique referred to as home networking is widely used. This technique involves the coupling of data processing devices by use of already existing cabling actually intended for other purposes. Since already existing cabling is used, such as for example domestic telephone and/or power supply cabling, no additional laying of connecting cables is required for connecting up data-processing systems within the range of the existing cabling.
For data transmission between the data processing devices connected up in this way, data packets to be transmitted are coded into signals outside a frequency range used for the actual intended purpose of the cabling and are fed into the cabling. In home networking via existing telephone cabling, for example, a frequency range not used by the telephone service of 5.5 MHz to 9.5 MHz is used for the transmission of data packets, so that telephone conversations simultaneously conducted via the telephone line are not adversely affected by this.
If a direct connection of the telephone line of a building, for example to an Internet service provider, exists, and this connection does not exceed a prescribed length, a home network can be linked up to other communication networks, such as for example the Internet, without additional devices being interposed by a user. However, on account of a relatively short range of the home network, this possibility often does not exist. This is particularly the case if the telephone cabling of a building networked in this way is connected to the public network via a commercially available switching system, such as for example a private branch exchange. The signals fed into the telephone cabling in the course of home networking are generally not transmitted into the public network by a commercially available switching system.
A generally applicable method of coupling a home network to a higher-level communications network is to connect a specific modem between the home telephone cabling and a public network, which carries out a conversion between a home network protocol and an integrated systems digital network (ISDN) protocol. However, a link-up via a specific modem has little flexibility, in particular with regard to relatively complex network structures.
As an alternative to this, a gateway computer with an ISDN plug-in card and a home-network plug-in card may be used together with associated routing software for the linking up of a home computer. However, this requires very high expenditure on hardware and protocol.